Friday, November 7, 2014

You’ve doubtless seen the pigeons feeding in the city square
or along the freeways roosting on light standards and nesting under the
overpasses. These are Rock Pigeons (Columba
livia), formerly called Rock Doves, and they are native to Eurasia but have
been introduced all over the world, first as captive birds and then established
in cities, towns and the countryside outside of captivity. They are
rock-dwelling birds that nest on cliffs, and they see our city buildings and
barns as just another kind of cliff.

However, we also have a bona fide wild pigeon in the Pacific Northwest, the Band-tailed Pigeon (Patagioenas fasciata). These are birds of the forest, birds that roost in trees and not on buildings. They are common west of the Cascades, occasionally seen on the east side. Many migrate south in autumn, but good numbers persist through the winter in areas where they can find food, both wild and human-provided.

We are fortunate that Band-tailed Pigeons are easily
attracted to bird feeders with mixed seeds, as they are really quite attractive
birds. They look something like Rock Pigeons but are slightly
longer-tailed and rounder-winged, evident when they fly overhead. They are gray
above, with more reddish underparts and a dark band bordered by a pale tip on
the tail (thus the name). The bill and feet are bright yellow, and there is a
white half-collar on the neck with an iridescent patch of feathers behind it.

These pigeons are vegetarians with a varied diet. Their
range coincides with the range of oak trees throughout much of the West, and
they eat a lot of acorns. But they also take pine nuts, fruits of all kinds,
seeds of herbaceous plants, especially grains, and a variety of buds and
flowers.

Band-tails build flimsy nests of twigs well up in trees,
averaging about 10 meters but up to 50 meters above the ground. The nest is
usually on a firm limb not far from the trunk. They lay a single egg, quite
unusual among pigeons and doves, which usually lay two. The egg is incubated alternately
by both male and female for about 18 days to hatching.

Both parents produce “pigeon’s milk,” a curdlike substance
that sloughs off from the inner walls of the crop (production mediated by
prolactin, just as in mammalian milk!); this is unique to pigeons. The young bird
(“squab”) remains in the nest for three or more weeks and may be fed by the
adults after it fledges.

There has been an uptick of interest in Band-tailed Pigeons
in recent years. A group of researchers are committed to de-extinction of the
Passenger Pigeon (Ectopistes migratorius),
and they are moving rapidly toward that goal. Their method involves working out
the genomes of both species and the systematic replacement of Band-tailed
Pigeon with Passenger Pigeon genes: “converting viable Band-tailed DNA to
viable Passenger Pigeon DNA.” They have now fully sequenced both species, so
stay tuned!

On October 30, a juvenile Band-tailed Pigeon landed on the feeder right
in front of me, and it looked just enough like a Passenger Pigeon, not seen alive
for over a century, that a chill ran over me.

Tuesday, November 4, 2014

Mergansers are fish-eating ducks. They are closely related
to Buffleheads and goldeneyes, but because they diverged sharply from their
invertebrate-eating relatives, their anatomy has diverged sharply as well. The main
point of divergence is in the bill. Buffleheads have a normal duck-shaped
bill, only 2-3x as long as wide.

A merganser bill, on the other hand, may be 4x as long as
wide. But more than that, the structure of the bill has changed dramatically.
Duck bills have plates or lamellae, fine transverse ridges on the cutting edges
that let water escape from the bill when prey is brought to the surface. In
mergansers, these plates have been modified to produce a saw-toothed effect.
These aren’t true teeth, lacking in birds, but they are very toothlike,
analogous to the teeth of barracudas, needlefish and dolphins, other
fish-catching vertebrates.

We have three kinds of mergansers in the Pacific Northwest. Two
of them are in the genus Mergus, the
Common Merganser (M. merganser) and
Red-breasted Merganser (M. serrator).
Both of them are large ducks, the Common one of our largest. Both have
relatively long, slender bills the edges of which look like saw blades. These
toothy bills are perfectly adapted for capturing slippery fish, and mergansers
feed only on fish.

The Common breeds in rivers all over the Northwest and
extends its range in winter to lakes and marine environments, especially deep
channels with swift currents. The Red-breasted breeds in the Arctic and
Subarctic and descends on the PNW in the winter, primarily on salt water. It is
one of the common and widespread wintering ducks on Puget Sound.

Both of these mergansers move around the landscape looking for fish, especially
fish in large schools that are easier to capture than the individual fish that
the ducks encounter most of the time. Thus herrings and sand lance, two of our
common schooling fishes, are often prey. Like other ducks, these mergansers may
be in flocks.

The Red-breasted is perhaps even better adapted as a fishing duck than the
Common, as its bill is a bit more slender and cylindrical. The bills of these
two duck species have converged on those of other fish-eaters such as loons,
grebes and cormorants, but none of the latter have the “teeth.”

The least modified and smallest of the mergansers is the
Hooded (Lophodytes cucullatus). It is
close enough to the goldeneyes (Bucephala)
to have hybridized with both Common Goldeneye (B. clangula) and Bufflehead (B.
albeola) and is considered intermediate between the goldeneyes and the
other mergansers.

The bill of the Hooded is also intermediate, with the “teeth” rounded or square
and nowhere nearly as impressive as in the other mergansers. The species may
eat as many invertebrates as fishes, especially crustaceans such as crayfish
and aquatic insects. It is much more confined to fresh water than the other
two, but small numbers winter in protected bays.

All three mergansers have nesting habits like the goldeneye group. Hooded
Mergansers nest in tree holes like Buffleheads and goldeneyes, Common
Mergansers, much larger, need much larger crevices in trees, but like Hooded,
sometimes uses old Pileated Woodpecker holes. On the other hand, Red-breasted
Mergansers nest on the ground, often in the shelter of rocks or fallen trees
adjacent to their preferred breeding wetlands. With their northerly breeding
range, there aren’t many trees big enough for a nest hole!

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About the Slater Museum

Our goals are to preserve and provide a collection of specimens to be used for research and education. Located in Tacoma, Washington, the Slater Museum is one of the region's significant repositories for bird, mammal, reptile, amphibian and plant specimens from the Pacific Northwest. In addition, we strive to educate the local community about nature and about the value of museums.